The steering knuckle assembly (wheel spindle assembly) of a motor vehicle includes a steering knuckle having a kingpin joint which receives an end of the steer axle. A kingpin (spindle bolt) is then inserted through bores in the kingpin joint and a bore coaxially aligned in the steer axle end, thereby pivotally securing the axle to the steering knuckle. The kingpin is a pivot axis around which the steering knuckle may move with respect to the axle. Such a design is common in motor trucks of the light to heavy-duty class.
In order for the steering knuckle to pivot and rotate, lubrication is provided in the knuckle joint bores. However, possible contamination may enter the joint, among other places, where the axle beam cooperates with the knuckle. While seals are presently used, they are not able to effectively keep contamination, water, and other foreign matter out of the bearing joint, while ensuring that the joint remains properly lubricated. This often leads to relubrication of the joints at frequent intervals, resulting in greater costs and increased labor associated with maintaining the steering assembly. Also, the potential contamination of the knuckle joint may reduce the life of the kingpin, associated bearing surfaces and other kingpin joint components, which may further lead to premature wear and possible replacement of the kingpin joints.
Moreover, the associated steer axle beam deflects under load, producing a pressure differential in the kingpin joint bearing areas. This pressure differential tends to pull contamination into the kingpin joint and bearings, thus reducing the life of the bearings and other kingpin joint components and again, resulting in frequent relubrication or potential replacement of parts due to wear and insufficient lubrication.
Various references have attempted to provide lubrication to a steering knuckle. For example, U.S. Pat. No. 4,043,567 issued to Kaiser discloses a steering axle assembly having a system for ensuring that lubricant has passed completely to the outer ends of the kingpin. An end plate having a check valve is provided in this reference, whereby the check valve allows grease to pass outwardly when there is sufficient lubrication in the kingpin receiving bores. This reference further discloses a disc-type plug which is flattened into position on the lower end of the lower yoke to prevent the flow of lubricant therefrom. However, this design does not prevent contamination from being drawn into the knuckle.
Further, U.S. Pat. No. 3,659,869 issued to Hase et al. discloses an axle spindle bearing assembly which includes a lower and upper bearing connected to each other by a bore system provided in the axle spindle bolt. A reservoir space connected to the bore system is arranged in the axle spindle bolt within the area of the upper bearing which is in communication with the section of the bore system leading to the lower bearing, for example, by way of a return checking device. However, this arrangement is costly in terms of tooling, manufacturing and piece price.
Consequently, the need has developed for an improved kingpin joint of a steering knuckle assembly which provides additional protection against the introduction of contamination and other foreign matter and allows for better long-term grease retention and lubrication of the joint. The kingpin joint should also be provided with a dedicated seal for when the steer axle and associated components deflect under service loads.